This proposal is a continuation of the previously awarded grant by National Cancer Institute dealing with molecular and electronic structure studies of a series of compounds which are of biological interest by electron diffraction and molecular quantum mechanical method. Various N-oxides as well as purine-oxides have been chosen for investigation. The first part of this project, the development and revision of various computational programs for electron diffraction analysis and quantum mechanical calculations, has been completed. We are continuing the second part of this project, the investigation of molecular and electronic structures of the proposed heterocyclic N-oxides. The parent compound of the N-oxide, pyridine-N-oxide, has been completed and reported. Other substituted pyridine-N-oxides, such as 4-chloropyridine-N-oxide, 4-methyl-pyridine-N-oxide, and 4-nitropyridine-N-oxide, are at the final stage of structural analysis. The molecular and electronic studies will aid in the understanding of the chemical and biological activities. BIBLIOGRAPHIC REFERENCE: Joseph F. Chiang, R. Chiang and M.T. Kratus, The Average Structures of 2.3-Diazabicyclohepta-2-ene and 2,3-Diazabicycloocta-2-ene, J. Mol. Struct. 26, 175 (1975).